Embedded clusters in giant extragalactic H II regions, 1: BVRH-alpha photometry

Abstract

Photometry in BVR continuum bands and in the emission line of H-alpha+(N II) are presented for a sample of H II complexes in disk, spiral arm and nuclear regions of galaxies NGC 1365, 1566, 2366, 2903, 2997, 3351, 4303, 4449, and 5253. Main sources of errors on H II region photometry are discussed. Errors due to background subtraction are parametrized in terms of background nonuniformity and fractional background contribution and are described separately in the Appendix. Our photometric data are compared with the existing data in the literature. Photometric properties of the sample regions are analyzed statistically and its implications on star formation are briefly discussed. Colors and H-alpha+(N II) equivalent widths of nuclear H II regions are found to be distinctly different from disk H II regions, suggesting different star formation histories. We have identified a few high H-alpha+(N II) equivalent width regions, which are fainter than average in both emission line and continuum fluxes, thus accounting for the low frequency of occurrence of such regions in flux limited samples.